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Subject[patch 10/11] tape: fix race with stack local wait_queue_head_t.
From: Martin Schwidefsky <schwidefsky@de.ibm.com>

A wait_event call with a stack local wait_queue_head_t structure that is
used to do the wake up for the wait_event is inherently racy. After the
wait_event finished the wake_up call might not have completed yet.
Replace the stack local wait_queue_head_t in tape_do_io and
tape_do_io_interruptible with a per device wait queue.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
drivers/s390/char/tape.h | 3 +++
drivers/s390/char/tape_core.c | 16 +++++++---------
2 files changed, 10 insertions(+), 9 deletions(-)
Index: quilt-2.6/drivers/s390/char/tape_core.c
===================================================================
--- quilt-2.6.orig/drivers/s390/char/tape_core.c
+++ quilt-2.6/drivers/s390/char/tape_core.c
@@ -449,6 +449,7 @@ tape_alloc_device(void)
INIT_LIST_HEAD(&device->req_queue);
INIT_LIST_HEAD(&device->node);
init_waitqueue_head(&device->state_change_wq);
+ init_waitqueue_head(&device->wait_queue);
device->tape_state = TS_INIT;
device->medium_state = MS_UNKNOWN;
*device->modeset_byte = 0;
@@ -954,21 +955,19 @@ __tape_wake_up(struct tape_request *requ
int
tape_do_io(struct tape_device *device, struct tape_request *request)
{
- wait_queue_head_t wq;
int rc;

- init_waitqueue_head(&wq);
spin_lock_irq(get_ccwdev_lock(device->cdev));
/* Setup callback */
request->callback = __tape_wake_up;
- request->callback_data = &wq;
+ request->callback_data = &device->wait_queue;
/* Add request to request queue and try to start it. */
rc = __tape_start_request(device, request);
spin_unlock_irq(get_ccwdev_lock(device->cdev));
if (rc)
return rc;
/* Request added to the queue. Wait for its completion. */
- wait_event(wq, (request->callback == NULL));
+ wait_event(device->wait_queue, (request->callback == NULL));
/* Get rc from request */
return request->rc;
}
@@ -989,20 +988,19 @@ int
tape_do_io_interruptible(struct tape_device *device,
struct tape_request *request)
{
- wait_queue_head_t wq;
int rc;

- init_waitqueue_head(&wq);
spin_lock_irq(get_ccwdev_lock(device->cdev));
/* Setup callback */
request->callback = __tape_wake_up_interruptible;
- request->callback_data = &wq;
+ request->callback_data = &device->wait_queue;
rc = __tape_start_request(device, request);
spin_unlock_irq(get_ccwdev_lock(device->cdev));
if (rc)
return rc;
/* Request added to the queue. Wait for its completion. */
- rc = wait_event_interruptible(wq, (request->callback == NULL));
+ rc = wait_event_interruptible(device->wait_queue,
+ (request->callback == NULL));
if (rc != -ERESTARTSYS)
/* Request finished normally. */
return request->rc;
@@ -1015,7 +1013,7 @@ tape_do_io_interruptible(struct tape_dev
/* Wait for the interrupt that acknowledges the halt. */
do {
rc = wait_event_interruptible(
- wq,
+ device->wait_queue,
(request->callback == NULL)
);
} while (rc == -ERESTARTSYS);
Index: quilt-2.6/drivers/s390/char/tape.h
===================================================================
--- quilt-2.6.orig/drivers/s390/char/tape.h
+++ quilt-2.6/drivers/s390/char/tape.h
@@ -231,6 +231,9 @@ struct tape_device {
/* Request queue. */
struct list_head req_queue;

+ /* Request wait queue. */
+ wait_queue_head_t wait_queue;
+
/* Each tape device has (currently) two minor numbers. */
int first_minor;

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.



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